Driving force transmission device and image forming apparatus using the same

ABSTRACT

A driving force transmission device that transmits a driving force to a rotation body includes a flange member provided in the rotation body, a through shaft that is connected to the flange member to transmit the driving force to the rotation body via the flange member, and an intermediate transmission member that is provided in the through shaft to transmit the driving force to the flange member from the through shaft.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims priority to Japanesepatent application No. 2015-015062, filed Jan. 29, 2015, the disclosureof which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to a driving force transmission device andan image forming apparatus using the same.

2. Description of Related Art

An image forming apparatus including a unitized consumable componentsuch as a photoconductor drum has been known. Such a unitized consumablecomponent is removably attached to the main body (hereinafter referredto as an apparatus body) of the image forming apparatus to be exchangedby a user. For example, each of a photoconductor drum, charging device,developing device, and cleaner is unitized to be removed from theapparatus body, and a driving force is transmitted to these units fromthe apparatus body. A tandem image forming apparatus includes four imageforming units corresponding to the four colors of yellow, magenta, cyan,and black. These image forming units are attached to the apparatus body,so that photoconductor drums, development rollers, and the like rotateto form an image. The apparatus body also includes a motor and a speedreduction unit which are driving sources for rotating the photoconductordrum, the development roller, and the like. The speed reduction unit isconnected to the photoconductor drum to transmit driving force.

Various connection members between the speed reduction unit and thephotoconductor drum have been proposed. For example, a spline couplingusing an external gear and an internal gear has been proposed. Since theimage forming unit is removably attached to the apparatus body, when thephotoconductor drum and the speed reduction unit are connected by thisspline coupling, eccentricity and a deflection angle occur between theoutput shaft of the speed reduction unit provided in the apparatus bodyand the shaft of the photoconductor drum attached to the speed reductionunit. Such eccentricity and a deflection angle also occur between theshafts of the external gear and the internal gear.

An image forming apparatus described in Patent Literature 1 (JapanesePatent No. 4775947) includes a serration coupling using a guide member.However, since such a serration coupling does not have a configurationwhich absorbs shift and eccentricity between a driving shaft and adriven shaft, an axis reaction force may occur due to a variation incomponent accuracy, resulting in deterioration in rotation of a drivingtarget.

An image forming apparatus described in Patent Literature 2 (JapaneseLaid-Open Patent Application No. 2007-240007) has a configuration whichabsorbs such shift and misalignment between a driving shaft and a drivenshaft. A parallel pin is pressed into the driving shaft and the drivenshaft, and an intermediate body engaging with the pin is held to reducethe axis reaction force due to a variation in component accuracy.However, such a configuration doubles the rotation irregularity sincethe driving force is transmitted by the two positions of the top andbottom portions of the parallel pin.

Patent Literature 3 (Japanese Laid-Open Patent Application No.2014-142431) describes a configuration in which crowned teeth of aninternal gear and an external gear of an intermediate body engage withan internal gear of a flange and a sintered gear pressed into a drumshaft, respectively, so as to reduce the axis reaction force in theengagement portions. However, in order to hold the intermediate body, animage forming apparatus described in Patent Literature 3 requires aninternal gear flange having a member for determining a coaxial level anda member for retaining the intermediate body to be pressed into a drum.Consequently, such an image forming apparatus has a problem in anassembly performance, and may deteriorate highly accurate straightnessand deflection that are required for a drum such as a photoconductordrum.

Patent Literatures 3 describe a technique using a two-stage spline jointincluding a flexible intermediate body having a crowned external gear toimprove rotation irregularity by dispersing load with the increasednumber of driving force transmission portions (teeth number). However,when this configuration is applied to the flange of the drum such as aphotoconductor drum, it is difficult to provide the crowed external gearto the drum in view of a layout.

SUMMARY

An object of the present invention is, therefore, to provide a drivingforce transmission device and an image forming apparatus using aconnection structure between a through shaft which penetrates through adevice such as an image forming unit and a rotation body of the imageforming unit. The connection structure achieves a reduced space and areduced axis reaction force in view of an assembly performance of arotation body.

To achieve the above object, an aspect of the present invention providesa driving force transmission device that transmits a driving force to arotation body. The device includes a flange member provided in therotation body, a through shaft that is connected to the flange member totransmit the driving force to the rotation body via the flange member,and an intermediate transmission member that is provided in the throughshaft to transmit the driving force to the flange member from thethrough shaft. The flange member includes a coaxial level control holethat controls a coaxial level with the through shaft, a cylindricalportion that extends in an axis direction to control a squareness to thethrough shaft, a thrush portion that controls movement in the axisdirection, and an internal gear having teeth extending in the axisdirection. The through shaft includes a parallel pin pressed in avertical direction of the shaft and a thrust member that controls athrust direction of the rotation body by contact with the thrustportion. The intermediate transmission member includes an external gearthat engages with the internal gear, a driving force receiving groovethat receives the driving force from the parallel pin pressed into thethrough shaft, and an inner diameter portion having a space relative toan outer circumference portion of the through shaft while beingsupported to move the through shaft in the axis direction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a general configuration of a copier as an imageforming apparatus to which a driving force transmission device accordingto an embodiment of the present invention is applied;

FIG. 2 is a view showing an image forming unit using a connectionstructure according to the embodiment of the present invention;

FIG. 3 is a view showing a configuration of a photoconductor drum in adrum joint according to the embodiment of the present invention;

FIG. 4 is a view showing a configuration of a drum shaft in the drumjoint according to the embodiment of the present invention;

FIG. 5 is a view showing a configuration of a clearance between the drumshaft and an intermediate transmission member according to theembodiment of the present invention; and

FIG. 6 is a view showing a U type groove of the intermediatetransmission member according to the embodiment of the presentinvention.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings. The embodiment of the present inventionuses a spline joint including a through shaft, which is applied to aconnection portion in an image forming apparatus, and has the followingfeatures. The embodiment describes an intermediate transmission memberthat is flexibly movable to an axis reaction force occurred in anengagement portion when transmitting driving force to a flange of aphotoconductor drum, so as to reduce the axis reaction force as much aspossible. The embodiment also describes a configuration which preventsthe surface of the photoconductor drum from being affected by the axisreaction force in the drum flange.

FIG. 1 is view showing a general configuration of a copier as an imageforming apparatus to which a driving force transmission device isapplied. The apparatus shown in FIG. 1 is a tandem electrophotographiccolor copier, and performs a process of visualizing an electrostaticlatent image with a two-component developing method using drytwo-component developer. In this embodiment the driving forcetransmission device is applied to the copier, but the driving forcetransmission device may be applied to a printer, facsimile, printingmachine, a multifunction machine, and the like.

The copier shown in FIG. 1 performs an image forming process byreceiving image data of image information from a not-shown image reader.The copier includes four photoconductor drums 1Y, 1M, 1C, and 1Bk whichare arranged in parallel and are latent image carriers as rotationbodies for four colors of yellow (Y), magenta (M), cyan (C), and black(Bk). These photoconductor drums 1Y, 1M, 1C, and 1Bk are arranged alonga belt moving direction to have contact with an endless intermediatetransfer belt 5 supported by a plurality of rollers including a drivingroller.

Each of the photoconductor drums 1Y, 1M, 1C, and 1Bk includestherearound an charging device 2Y, 2M, 2C, and 2Bk, a developing device9Y, 9M, 9C, and 9Bk, a cleaner 4Y, 4M, 4C, and 4Bk, and a neutralizer3Y, 3M, 3C, and 3Bk. These devices for an electrophotographic processare provided in accordance with an order of a process. Each of thephotoconductor drums 1Y, 1M, 1C, and 1Bk is detachably attached to anapparatus body in the axis line direction.

Hereinafter, a process of forming a full color image with the copiershown in FIG. 1 will be described. The photoconductor drum 1Y isuniformly charged by the charging device 2Y while rotating in the arrowdirection in FIG. 1 with the after-described photoconductor drum driver.After that, the photoconductor drum 1Y is irradiated with a light beamLY from a not-shown optical writer to form a Y electrostatic latentimage. The Y electrostatic latent image is developed by Y toner of adeveloper by the developing device 9Y. In developing, a predetermineddevelopment bias voltage is applied between the development roller andthe photoconductor drum 1Y, and the Y toner on the development roller iselectrostatically absorbed to the Y electrostatic latent image on thephotoconductor drum 1Y.

A Y toner image formed as described above is fed to a first transferposition where the photoconductor drum 1Y has contact with theintermediate transfer belt 5 along the rotation of the photoconductordrum 1Y. A predetermined bias voltage is applied to the rear surface ofthe intermediate transfer belt 5 in the first transfer position by aprimary transfer roller 6Y. The Y toner image on the photoconductor drum1Y is transferred onto the intermediate transfer belt 5 by a primarytransfer electric field generated by the application of the biasvoltage. An M toner image, C toner image, and Bk toner image aresequentially transferred onto the Y toner image on the intermediatetransfer belt 5 to be superimposed in the same manner.

The superimposed toner images on the intermediate transfer belt 5 arefed to a second transfer position facing a secondary transfer roller 7along the rotation of the intermediate transfer belt 5. A transfer sheetis fed to the second transfer position by a not-shown registrationroller in predetermined timing. A predetermined bias voltage is appliedto the rear surface of the transfer sheet by the secondary transferroller 7 in the second transfer position, and the toner images on theintermediate transfer belt 5 are all secondary transferred onto thetransfer sheet by the secondary transfer electric field generated by theapplication of the bias voltage and the contact pressure in the secondtransfer position. After that, the transfer sheet onto which the tonerimages are secondary transferred is discharged outside after a fixingprocess with a pair of fixing rollers 8.

FIG. 2 is a view showing the image forming unit using a connectionstructure according to the embodiment of the present invention. FIG. 3is a view showing a configuration of the photoconductor drum in a drumjoint according to the embodiment of the present invention. Thephotoconductor drum in the image forming apparatus such as a printer anda photoconductor driving shaft provided in the apparatus body aredescribed with reference to FIGS. 2 and 3. In this embodiment, thephotoconductor drum is described as a driven body. However, theembodiment of the present invention can be applied to a transfer roller,development roller, and cleaning roller which have a through shaft, forexample.

Since the photoconductor drums 1Y, 1M, 1C, and 1Bk are rotated byphotoconductor drivers each having the same configuration, respectively,the connection between the photoconductor drum 1Y and the photoconductordriver will be hereinafter described. As illustrated in FIG. 1, thephotoconductor drum 1Y is attached to the apparatus body, and thephotoconductor drum 1Y is supported by a drum shaft 50Y (through shaft),as illustrated in FIG. 2. The drum shaft 50Y is a metal shaft, forexample.

A drum flange 51 is pressed into the photoconductor drum 1Y, as shown inFIG. 3. The drum flange 51 is a flange member into which the drum shaft50Y is fitted with high accuracy. The drum flange 51 has a through hole52 that controls straightness and deflection of the drum shaft 50Y ofthe photoconductor drum 1Y when the drum shaft 50Y is fitted into thethrough hole 52. Namely, the through hole 52 is a coaxial level controlhole that controls the coaxial level between the through hole 52 and thedrum shaft 50Y. In order to improve the deflection and the straightnessof the photoconductor drum 1Y after the drum flange 51 is pressed into atube 53 of the photoconductor drum 1Y, the drum flange 51 is required tobe secondary processed. The drum flange 51 therefore includes aprotrusion 54 that is chucked by a machining tool.

An internal gear 55 including teeth extending in the axis direction ofthe drum shaft 50Y is provided inside the protrusion 54. The drum flange51 is driven by the internal gear 55, so that the photoconductor drum 1Yrotates. A web face 56 of the drum flange 51 is formed in the endportion of the internal gear 55. Even when the axis reaction forceoccurs in the internal gear 55, such a force is barely conveyed to theweb face 56. Consequently, the surface of the photoconductor drum 1Y isprevented from being vibrated. The through hole 52 includes acylindrical portion 57 having a sufficient length on the opposite sideof the internal gear 55. The cylindrical portion 57 extends in the axisdirection of the drum shaft 50Y to control the squareness of the drumshaft 50Y. Even when the axis reaction force occurs in the internal gear55, the web face 56 hardly falls. The surface of the photoconductor drum1 is therefore prevented from being vibrated in rotation.

FIG. 4 is a view showing the configuration of the drum shaft in a drumjoint according to the embodiment of the present invention. FIG. 5 is aview showing a space (clearance) between the intermediate transmissionmember and the drum shaft. FIG. 6 is a view showing a U type groove ofthe intermediate transmission member according to the embodiment of thepresent invention.

A thrust member 60 that determines a thrust position of the drum flange51 is pressed into the drum shaft 50Y. The thrust member 60 has contactwith the end portion of the through hole 52 of the drum flange 51,namely, a thrust portion to determine the position of the photoconductordrum 1Y in the thrust direction.

An intermediate transmission member 62 having an external gear 61 isheld in the drum shaft 50Y. As illustrated in FIG. 5, a sufficientclearance 63 is provided between an inner diameter portion of theintermediate transmission member 62 and an outer circumference portionof the drum shaft 50Y. The intermediate transmission member 62 thereforefreely moves (refer to FIG. 6). By separately manufacturing the thrustmember 60 and the drum shaft 50Y as the through shaft, the material andprocessing costs of the drum shaft 50Y can be lowered. It is preferablefor the thrust member 60 to be a sintered member. A strength requiredfor supporting load in the thrust direction can be obtained by thesintered member.

It is preferable for the teeth of the external gear 61 and the internalgear 55 to have sufficient backlash at a pressure angle of 30°. With thepressure angle of 30°, the strength in the tooth root is improved toincrease durability. The sufficient backlash is thereby obtained betweenthe gears. The intermediate transmission member 62 therefore freelytilts in the engagement position of the external gear 61 and theinternal gear 55, and thus, the misalignment absorption performance isimproved to easily reduce the axis reaction force. It is preferable forthe end portions of the teeth on the engaging gear side between theexternal gear 61 and the internal gear 55 to have a tapered shape forsmoothly and repeatedly attaching and removing the image forming unitincluding the photoconductor drum 1Y. The tapered shape is often used asa joint. One of the teeth can be set as a tooth to be firstly engagedfor improving an engagement performance. For example, it is preferablefor one of the teeth of the internal gear 55 to have a width larger thanthose of the other teeth.

In the above embodiment, the drum flange 51 is driven via the externalgear 61 of the intermediate transmission member 62. However, theeccentricity occurs between the internal gear 55 of the drum flange 51and the external gear 61 of the intermediate transmission member 62 fora processing reason. Consequently, the center of the internal gear 55and the center of the external gear 61 are always misaligned. It isnecessary to absorb such eccentricity by the tilt of the intermediatetransmission member to transmit a highly accurate driving force. Asdescribed above, the sufficient clearance 63 is provided between theinner diameter portion of the intermediate transmission member 62 andthe outer circumference portion of the drum shaft 50Y. It is necessaryfor the clearance 63 to ensure a size that sufficiently absorbs theabove eccentricity (refer to FIG. 5). The intermediate transmissionmember 62 includes in the outer circumference thereof a U type groove 66extending along the axis direction. The intermediate transmission member62 is made of a resin material or a sintered material. When theintermediate transmission member 62 is made of the sintered member andsuch a member requires a secondary process, the costs for manufacturingthe member are increased. However, when the U type groove 66 has aconstant length or below, the secondary process is not required. Thus,an increase in cost can be controlled.

A parallel pin 65 is fitted into the U type groove 66. The U type groove66 receives the driving force from the parallel pin 65 as a drivingforce receiving groove. The parallel pin 65 is pressed into the drumshaft 50Y in the vertical direction of the axis, and is a positioningpin provided to protrude outside in the diameter direction. Grease maybe applied to the parallel pin 65 for further reducing the axis reactionforce by reducing the contact friction between the U type groove 66 andthe parallel pin 65. However, a defect image is generated when thegrease is dispersed onto the image forming region of the photoconductordrum 1Y. To prevent this dispersion, the protrusion 54 illustrated inFIG. 3 has a length that covers the parallel pin 65. Namely, theprotrusion 54 is a cylindrical portion provided in the teeth end portionof the internal gear 55 of the drum flange 51, having a diameter largerthan that of the teeth bottom of the internal gear 55, and having ashape that covers the upper portion of the parallel pin 65. Theprotrusion 54 covers the parallel pin 65 even when the grease is appliedto the parallel pin 65. The grease is thus prevented from beingdispersed onto the image forming region of the photoconductor drum 1Y.As illustrated in FIG. 5, a pair of parallel pins 65 is provided insymmetry positions of the external gear 61 in the diameter direction.However, the parallel pins 65 may be provided in another position, or asingle parallel pin 65 may be provided.

As described above, the embodiment of the present invention uses aso-called two-stage spline coupling. Namely, the drum flange 51 includesthe through hole 52 for positioning the drum shaft 50Y as the throughshaft. The through hole 52 includes the cylindrical portion 57 having asufficient length. The drum flange 51 also includes the thrust portion60 as a thrust stop mechanism, and the internal gear 55 for transmittingthe driving force to the photoconductor drum 1Y. The web face 56constituting the web position is provided in the end portion of theinternal gear 55.

The drum shaft 50Y includes the thrust member 60 as a thrust stopmechanism of the drum flange 51 in the axis direction and theintermediate transmission member 62 having the external gear 61 engagingwith the internal gear 55 of the drum flange 51. The drum shaft 50Y alsoincludes the parallel pin 65 pressed into the shaft to transmit thedriving force to the intermediate transmission member 62. Theintermediate transmission member 62 includes the clearance 63 betweenthe outer diameter portion of the drum shaft 50 and the inner diameterportion of the intermediate transmission member 62 to sufficientlyabsorb the misalignment.

Therefore, the drum assembly component is positioned in the through hole52 relative to the drum shaft 50Y, and is supported by the cylindricalportion 57 having a sufficient length. The drum flange 51 is therebyprevented from being tilted, and the thrust direction is determined, sothat the image-forming region is stabilized.

The driving force of the drum shaft 50Y is supplied to the drum flange51 from the internal gear 55. Since a sufficient distance is providedbetween the web face 56 and one end portion of the internal gear 55, thedeformation of the drum flange 51 is barely affected to the web face 56.Thus, the straightness of the drum (photoconductor drum 1Y) ismaintained, and the surface of the drum (photoconductor drum 1Y) isprevented from being vibrated barely even when a load is applied to theend portion of the internal gear 55 from the drum shaft 50Y.

The position of the drum flange 51 is controlled by the thrust member 60of the drum shaft 50Y. The driving force is transmitted via the externalgear 61 of the drum shaft 50Y. The driving force is transmitted to theintermediate transmission member 62 for driving from the drum shaft 50Yvia the parallel pin 65. The misalignment such as shaft shift andeccentricity between the drum flange 51 and the drum shaft 50Y due to amachining accuracy of a component is absorbed by the tilt of theintermediate transmission member 62 in the clearance 63. Theintermediate transmission member 62 includes the clearance 63 to reducethe axis reaction force from the coupling portion. As described above, ahigh performance drum joint can be provided to the image formingapparatus.

According to the embodiment of the present invention, a highly accuratedriving force can be applied to the rotation body by the through shaftwithout deteriorating the speed fluctuation and the surface vibration ofthe rotation body due to the axis reaction force in the connectionportion between the rotation body and the through shaft.

Although the present invention has been described in terms of anexemplary embodiment, it is not limited thereto. It should beappreciated that variations or modifications may be made in theembodiment described by persons skilled in the art without departingfrom the scope of the present invention as defined by the followingclaims.

What is claimed is:
 1. A driving force transmission device thattransmits a driving force to a rotation body, the device comprising: aflange member provided in the rotation body; a through shaft that isconnected to the flange member to transmit the driving force to therotation body via the flange member; and an intermediate transmissionmember that is provided in the through shaft to transmit the drivingforce to the flange member from the through shaft, wherein the flangemember includes a coaxial level control hole that controls a coaxiallevel with the through shaft, a cylindrical portion that extends in anaxis direction to control a squareness to the through shaft, a thrushportion that controls movement in the axis direction, and an internalgear having teeth extending in the axis direction, the through shaftincludes a parallel pin pressed in a vertical direction of the shaft anda thrust member that controls a thrust direction of the rotation body bycontact with the thrust portion, and the intermediate transmissionmember includes an external gear that engages with the internal gear, adriving force receiving groove that receives the driving force from theparallel pin pressed into the through shaft, and an inner diameterportion having a space relative to an outer circumference portion of thethrough shaft while being supported to move the through shaft in theaxis direction.
 2. The driving force transmission device according toclaim 1, wherein teeth of the external gear and the teeth of the innergear have backlash at a pressure angle of 30°.
 3. The driving forcetransmission device according to claim 1, wherein the driving forcereceiving groove is a U type groove.
 4. The driving force transmissiondevice according to claim 1, wherein the thrust member is a sinteredmember, and is pressed into the through shaft.
 5. The driving forcetransmission device according to claim 1, wherein the flange member hasa cylindrical portion provided in a teeth end portion of the inner gear,and the cylindrical portion has a diameter larger than that of a teethbottom and a shape that covers an upper portion of the parallel pin. 6.The driving force transmission device according to claim 1, wherein ateeth end portion on an engaging side between the inner gear of theflange member and the outer gear of the intermediate transmission memberhas a tapered shape, and one of the teeth of the inner gear has a teethwidth larger than those of the other teeth.
 7. The driving forcetransmission device according to claim 1, wherein the rotation body is aphotoconductor.
 8. An image forming apparatus comprising the drivingforce transmission device according to claim 1.